1. Field of the Invention
Embodiments described herein relate to detecting and classifying particles in a liquid using multi-angle-light-scattering (MALS), and in particular to detecting and classifying biological agents, such as bacteria and bacterial spores, and to detecting other agents that can cause the destruction of natural bacterial particles normally present in water, such as chemical, biotoxin, or radiation agents.
2. Background of the Invention
A major concern for municipal and commercial water treatment facilities is the detection and control of pathogenic microorganisms, both known and emerging, in potable water treatment and distribution. There are not only a number of chlorine resistant pathogens such as Cryptosporidium that can contaminate drinking water systems, but also potentially harmful microorganisms that can be introduced, either accidentally or intentionally, and propagate under suitable environmental conditions. Due to the length of time for standard laboratory methods to yield results, typically 24-72 hours, there has not been a reliable system to detect microbial contaminants in real-time and on-line to provide a warning of pathogen contamination events. Because of these expanding challenges, there has been an accelerated development of rapid tests and real-time methods to address the pressing needs of the water treatment community.
Conventional microbiological methods can be used to detect some harmful microorganisms; however, such methods provide limited results. Analytical methods in microbiology were developed over 120 years ago and are very similar today. These methods incorporate the following steps: sampling, culturing and isolating the microbes in a suitable growth media by incubation, identifying the organisms through microscopic examination or stains, and quantifying the organisms. Cryptosporidium and Giardia form oocysts or cysts and cannot easily be cultured in conventional ways. To detect these protozoan pathogens, an amount of water containing suspected pathogens, typically 10 liters, is sent through a special filter to collect and concentrate the organisms. Then the filter is eluted and the organisms further processed by staining the organisms and sending the concentrated solution through flow cytometry for example. These procedures, which can be found in Standard Methods (EPA 16.23) or ASME, require ascetic technique in sampling and handling, skilled technicians to perform the analysis, and a number of reagents, materials, and instruments to obtain results. Practically, such methods have proved to be time consuming, costly, and of little effectiveness for many current environmental field applications.
In order to reduce the amount of time to access microbiological results, a number of methods have been developed, mostly in the field of medicine. These faster tests have been improved and adapted to the environmental field and are generally categorized as 1) accelerated and automated tests 2) rapid tests and 3) contamination warning systems (CWS).
Accelerated tests are by grab sample and results can be obtained in 4 hours to 18 hours. Accelerated tests include immunoassays, ATP luminescence, and fluorescent antibody fixation. Rapid tests are also by grab sample and require manipulation of the sample to ‘tag’ the microbes with an identifiable marker or concentrate the microbe's genetic material (DNA) for subsequent identification. Results are normally available in 1-3 hours. These types of tests include Polymerase Chain Reaction (PCR) and Flow Cytometry.
Real time contamination warning systems are continuous warning devices that detect contaminants and provide an ‘event’ warning within minutes to prompt further investigation or action. CWS include laser based multi-angle light scattering (MALS) and multi-parameter chemical & particle instruments that detect water quality changes inferring potential biological contamination. Continuous, real time detection of pathogens in water surveillance was first tried in the late 1960's and has progressed through a series of development steps until the first public field demonstration in 2002.
When light strikes a particle a characteristic scattering pattern is emitted. The scattering pattern encompasses many features of the particle including the size, shape, internal structures (morphology), particle surface, and material composition. Each type of microorganism will scatter light giving off a unique pattern herein called a Bio-Optical Signal (BOS). Photo-detectors collect the scattered light and capture the patterns which are then sent to a computer for analysis.
In addition to detecting biological pathogens in the water that occur naturally or are introduced intentionally by terrorists, it can be desirable to also monitor for the presence of toxins such as; microbial toxins for example, botulism; chemical toxins for example, Aldicarb, Nicotine, Cycloheximide, Sodium Arsenate, or Sodium Fluoroacetate; or radiation generating alpha, beta, or gamma radiation; any of which chemical, biological, or radiation (CBR) agents that may also be present.
Various sensors have been used to monitor water quality for chemical agent attack. Currently available water quality sensor technology is based generally on adaptations, modifications, and extensions of conventional analytical chemistry equipment and techniques. Some examples follow.
U.S. Pat. No. 5,965,882 issued on Oct. 12, 1999 to Megerle et al. describes a miniaturized ion mobility spectrometer sensor cell that comprised an improved spectrometer for detecting chemical warfare agents and hazardous vapors.
U.S. Pat. No. 5,922,183 issued on Jul. 13, 1999 to Rauh describes a metal oxide matrix. Thin film composites of the oxides and biological molecules such as enzymes, antibodies, antigens and DNA strands can be used for both amperometric and potentiometric sensing.
U.S. Pat. No. 5,866,430 issued on Feb. 2, 1999 to Grow describes a methodology and devices for detecting or monitoring or identifying chemical or microbial analytes. The described methodology comprises four basic steps: (1) The gas or liquid medium to be monitored or analyzed is brought into contact with a bioconcentrator which is used to bind with or collect and concentrate one or more analytes. (2) The bioconcentrator-analyte complex is then exposed to radiation of one or more predetermined wavelengths to produce Raman scattering spectral bands. (3) At least a portion of the Raman spectral bands is collected and processed by a Raman spectrometer to convert the same into an electrical signal. And (4) the electrical signal is processed to detect and identify, qualitatively and/or quantitatively, the analyte(s).
U.S. Pat. No. 4,906,440 issued on Mar. 6, 1990 to Kolesar describes a sensor for detecting chemicals. In this sensor a gas detector is described that detects the presences of the gas when the gas reacts with a distributed RC notch network to cause a shift in operating frequency and notch depth. A metallic/metallic oxide gas sensitive discontinuous film acts as the distributive resistive element in the RC notch network. The gas changes the conductivity of the film and this causes the network to react. In the preferred embodiment, a copper/cuprous oxide film detects organophosphorus compounds, which can be chemical warfare agents.
U.S. Pat. No. 4,752,226 issued on Jun. 21, 1988 to Akers et al. describes a method for simulating chemical warfare attack that includes the use of a radiant energy transmitting device for radiating energy in a pattern which simulates different types and forms of chemical agents. Protective devices, such as gas masks, protective clothing, or structures, are provided with sensors for determining whether the protective device is properly employed.
U.S. Pat. Nos. 6,569,384 and 6,964,857 issued on May 27, 2003 and Nov. 15, 2005 respectively to Greenbaum et al. describe using changes in the natural fluorescence from naturally occurring organisms in the water to monitor for chemical attack.
All of these sensors and methods leave something to be desired in terms of accuracy, efficiency, cost or some combination thereof.
There are also many systems that measure gamma radiation directly in water, fewer that measure beta radiation, and still fewer that measure alpha radiation. Generally the alpha radiation detectors dry our a water sample and then measure the alpha radiation in air or vacuum.
Presently, a detection system capable of meeting all of the ‘ideal detection system’ parameters, e.g., as cited by the American Water Works Association does not exist. Conventional devices and methods often differ in the amount of time to obtain results, degree of specificity, sampling frequency, concentration sensitivity, operating complexity, and cost of ownership.